The most distinct feature of Gram positive bacteria are the presence of lipoteichoic acid and a membrane system consisting of a plasma membrane and mesosomes. The purpose of this project is to relate membrane structure with function using Staphylococcus aureus as the model test system. We have already shown by chemical analysis and serological methods on isolated fractions that the majority of the lipoteichoic acid is localized in the mesosomal portion of the membrane. This past year we have investigated some of the functions ascribed to lipoteichoic acid. Using purified preparations of lipoteichoic acid and derivatives prepared from S. aureus, and antisera prepared to the polyglycerolphosphate backbone portion of the lipoteichoic acid, we obtained evidence that this polymer may act as a protein carrier: more specifically, it carries streptolysis S, and it may also play a vital role in the adherence of bacteria to tooth surfaces.